B-cell acute lymphoblastic leukemia (B-ALL) is the most common cancer in children. The most high-risk B-ALL patients often have activated oncogenic kinases like BCR-ABL, PDGFR and JAK. These kinases converge on the PI3K/AKT/mTOR pathway, which promotes cancer cell proliferation and survival. The activity of this pathway correlates with poor outcome and higher relapse. The goal of this project is to determine the potential therapeutic benefits of various inhibitors of this pathway when combined with the current chemotherapeutic agents. However, our pilot studies have revealed that inhibition of mTOR actually induces chemotherapeutic resistances whereas PI3K or AKT inhibitors tend to enhance B-ALL killing. Our first aim is to determine which PI3K or AKT inhibitors combine best with chemotherapy to better kill B-ALL cell lines and primary patient leukemia cells. Moreover, we will determine if the addition of PI3K or AKT inhibitors can reduce relapse rates in xenograft models. Our second aim is to determine the mechanism of mTOR-induced chemoresistance to gain clues as to how this chemoresistance can be reversed. Our preliminary data also shows that the BCR- ABL inhibitor dasatinib can make cells resistant to methotrexate in cell lines where dasatanib also inhibits mTOR but not in cell lines where dasatinib does not inhibit mTOR. Thus our last aim is to determine if dasatinib also protects primary patient cells from methotrexate and if reduction in mTOR activity by dasatinib can serve as a biomarker to indicate if dasatinib should be combined with methotrexate. This study will not only guide the more effective use of PI3K/AKT/mTOR inhibitors in B-ALL, but also the current use of dasatinib in the clinic.